Apache Corp recently commenced horizontal drilling activity to develop shale gas reserves in Neuquen basin, Argentina. On one well, the curve was drilled with a 12¼-in PDC bit on PDM. The lateral was drilled with an 8½-in PDC on a point-the-bit RSS. A motor BHA was used in the curve because standard RSS could not deliver the required DLS. To optimized operations, Apache wanted to complete the curve and lateral with a single 8½-in PDC. However, the lack of high-build rate RSS required the curve still be drilled with a motor building to 50° then tripping for a point-RSS to TD the lateral. The single diameter strategy was successfully executed but further NPT reduction was still possible. The challenge was to drill the curve/lateral with a high build-rate RSS and a single 8½-in PDC in one run to eliminate a trip to change the drive system. The introduction of an inclination hold and azimuth software system would enable the RSS tool, created to build the aggressive curve angle, to continue efficiently drilling in the lateral saving an additional trip. An engineering analysis was then launched to design an application specific PDC for the RSS. A FEA-based system was employed to analyze offset BHAs, directional profiles, bit hydraulics and mud properties. The study revealed the baseline PDC was delivering excellent ROP in both the curve/lateral, but modifications would be required to increase the bit’s dynamic stability. A modified 8½-in SDi513 was proposed that features a customized cutting structure and tapered gauge for improved stability.

Next, a rock strength analysis was used to determine characteristics of lithologies encountered in the field. The study determined Quintuco (curve) and Vaca Muerta (lateral) have relatively low UCS (3-15 kpsi) but vibration potential in Quintuco is moderate. Computer simulations were run to map lateral/axial acceleration and bit torque on RSS. The results showed the new design displayed a significant increase in dynamic stability compared to the baseline bit with similar high ROP potential.

The shale optimized BHA drilled 1289-m of curve and lateral in one run at a record ROP of 9.64 m/hr, 35% faster than the offset average. The high build-rate RSS landed the wellbore at 96° with a maximum turning radius of 11.8°/30m increasing reservoir exposure within the acreage unit. The increased ROP enabled Apache to reach TD seven days ahead of plan for a savings of $595,000USD.

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